I have an 07 Sport Trac with 4.6 with #4 cylinder misfire. on 2007 Ford Explorer Sport Trac

So far I've changed out all plugs and coil packs for cylinders 4 and 8 because I retrieved codes P0304 and P0308 and P1000. My truck continues to throw P0304. I've also used an EXPENSIVE injector cleaner. What else can I do, Could you please help?